DESCRIPTION: The proposed work is to learn about basic principles of the interaction of cell surface adhesion receptors with counter receptors, ligands and viral proteins. It will also address aspects of membrane anchoring and signalling. He will study by NMR the solution structures of extra cellular domains of immune-cell surface protein receptors, their co-receptors and receptor/co-receptor complexes. This research will lead to an understanding of principles of receptor function, protein-protein recognition, receptor specificity and cell adhesion. It will include solving carbohydrate structures in intact glycoprotein domains. The work will initially focus on the structure refinement of the glycosylated adhesion domain of human CD2, a 13 kDa protein with a single N-linked high-mannose glycan. This glycan or part of it is crucial for the adhesion function of hCD2. Relaxation studies will map the relative mobility of different polypeptide and glycan parts. Next the interaction with the co-receptor CD58 will be characterized. For this purpose, the adhesion domain of CD58 will be expressed, and the structure of the adhesion domain will be solved by NMR. Following this, the structure of the receptor co-receptor complex (ca. 25 kDa) will be studied. As a related theme, the solution structure of the N-terminal two-domain 184-residue fragment of human CD4 will be solved to obtain a basis for binding studies with peptides from HIV gp 120 and major histocompatibility complex molecules. This will include studies of the internal mobility using 15N and relaxation experiments in order to explore whether increased or reduced mobility is relevant for the interaction with other proteins. This work will be complemented by solving the solution structure of a single-chain Fv fragment of a Dl0 T-cell receptor (TCR) of antigens. Finally, he will study the conformations of the small membrane-crossing segments of CD2, CD4 and the T-cell receptor using NMR experiments with isotope labelled peptides in perdeuterated micelles.